thanks lilkim!
i read your mentioned link,but there is some doubt for me!
what i actually found relavent to the question is :

At pH 4.8, the interior of the lysosomes is more acidic than the cytosol (pH 7). The lysosome single membrane stabilizes the low pH by pumping in protons (H+) from the cytosol, and also protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. For this reason, should a lysosome's acid hydrolases leak into the cytosol, their potential to damage the cell will be reduced, because they will not be at their optimum pH.

The constant pH of 4.8 is maintained by proton pumps and Cl- ion channels

i wana to know is this reason cause protecting the lysosome's membrane from being digested by ensymes too?
thanx in advance

The lysosomal membrane is primarily composed of lipids (phospholipids) and lysosomal protiens. Where as the enzymes enclosed by this vesicle only act at certain amino acid sequences of protiens.

Based on these facts I would assume that membrane bound lysosomal proteins do not contain these 'target' amino acid sequences and therefore would not be degrade by lysosomal enzymes. And I guess that the glycosylation (anti-degrative sugars) would further protect the lysomes from self-destruction.

I just have to say that I loved learning about lysosomes!! I think they're cool. In my AP bio class last year, we had to write a children's book using cell parts as characters. I made the lysosome look really cool

I'm guessing this topic is old and nobody is looking but just in case...I'm trying to figure out how M. tuberculosis kills macrophages and have some evidence that lysomes are damaged, releasing hydrolases that attack macrophage membranes (nuclear, mitochonrdrial, plasmalemmal). This relates to the original question here - how is the lysosomal limiting membrane protected from the internal hydrolases. It's really hard to find good answers to this. There is the mysterious "glycocalix" proteins but almost no references on a Pubmed search of lysosome + glycocalix. The lysosomes do indeed contain enzymes with phospholipase activity capable of damaging membranes, but these might not have access to the membranes without protein interactions. It seems that bits of intraluminal membrane are degraded in lysosomes. This process might require a unique acidic phosophlipid called bis(monoglycero)phosphate and an interaction with a saposin. Might be that the limiting membrane is sequestered from these systems that enable enzymatic attack on the internal membranes.

If anybody has any ideas about possible targets within the lysosome for some putative bacterial factor that would result in membrane destabilization I'd love to hear from you!

Inside the lysosome membrane there is a thick "glycocalix" protective layer.

This "glycocalix" is made of special proteins called "Lysosome associated membrane proteins (LAMP)" and sugars "polylactosamine."

Source: The lysosomal leaflet of the limiting membrane is covered with a thick glycocalix that protects the membrane from attack by the membrane-degrading enzymes present in the lysosol. This glycocalix is formed by lysosomal integral and peripheral membrane proteins, which are highly N-glycosylated with polylactosamine units and therefore highly resistant toward lysosomal digestion (Eskelinen et al. 2003).

Lysosomes are organelles of the cell that are not degraded themselves, they just degrade things. They also don't digest endosomes. Early endosomes are recycled back to plasma membrane to be reused in transporting more substances to them via the endocytic pathway, and late endosomes just transport the material to lysosome.Read more: http://www.madsci.org/posts/archives/20 ... .Cb.r.html